This invention relates to a partitioned display control system for controlling exhibition of different kinds of display on partitioned regions of a display surface of a refresh type display unit such as a CRT display unit with which an element such as a light pen can be used to renew or remove any desired portion of display.
A pattern display unit such a CRT display unit does not possess the function of storing information in itself. Such a pattern display unit is therefore generally provided with a refresh memory which has data storage locations or addresses corresponding in a one-to-one relationship to the unit display regions of the display surface, so that data stored in the storage locations or addresses can be read out in synchronism with scanning of the display surface of the CRT display unit. Display data which specifies characters such as letters or patterns to be displayed on the unit display regions is externally supplied to be written in this refresh memory. The display data is read out in synchronism with the scanning of the display surface of the CRT display unit, and this data is combined with a character signal generated by a character generator to provide a picture signal. This picture signal is displayed on the display surface of the CRT display unit in a conventional manner. Such display data, which is externally written in the refresh memory to be displayed on the display surface of the CRT display unit in usual manner, is generally called application display data, and this kind of display is generally called application display.
A keyboard or a light pen is commonly used for displaying a new character on the display surface or erasing a portion of characters displayed already on the display surface according to the application display. When the light pen is used for the above purpose, display of a group of light buttons to be pointed by the light pen, that is, special display is required. This special display generally comprises control display and marker display. The term "control display" refers to the display of a group of light buttons including a light button used for controlling the movement of a cursor specifying a unit display region of the application display area for displaying or erasing a character on or from the unit display region, a light button used for setting the size of a character to be displayed, a light button used for causing parallel movement of all the characters on the application display area, and a light button used for the selective display of a character block when a group of characters to be displayed on the application display area are divided into a plurality of blocks and one of these blocks is to be displayed. The term "marker display" refers to the display of a group of characters to be pointed by the light pen when desired characters are to be displayed on the application display area.
According to a prior art proposal which is directed to the control display and marker display required for pointing by the light pen, a hardware circuit associated exclusively with the light pen is provided independently of that associated with the aforementioned refresh memory so as to control the exhibition of the control display and marker display on the display surface of the CRT display unit.
In the case of such prior art proposal, however, the display system including the refresh memory used for the application display operates independently of the display system including the hardware circuit associated with the light pen used for the special display, so that the application display and special display are exhibited on the fixed display region of the CRT display unit. Therefore, the display surface of the CRT display unit must necessarily be distinctly partitioned into an application display region and a special display region. In other words, the display surface region available for the application display is limited due to the necessity for additional exhibition of the special display including the control display and marker display. Thus, the prior art proposal results in a great problem is that, on one hand, the display surface of the CRT display unit whose area is difficult to be increased is not fully effectively utilized for the application display, and on the other hand, part of the memory region of the refresh memory is left non-utilized.
According to another prior art proposal made in an attempt to solve the above problem, the refresh memory is adapted to store application display data in sufficient quantity to cover the entire display surface area of the CRT display unit, and the special display interrupts the application display under control of externally prepared software. In the case of this method, however, it is necessary to manage and control the operation to prevent concurrence of the special display and application display, and a very complex software program is required therefor. According to still another prior art proposal, a pair of refresh memories are provided to be used for the application display and special display, respectively. In the case of this last-mentioned method too, extreme difficulty is encountered in the preparation of a suitable software program and management of operation for preventing concurrence of the application display and special display, as in the former method.